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<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>

    let a = 1
    fn()

    function fn() {
      let a = 2
      fn2()
    }

    //函数的作用域查找是从函数声明的位置往外找，而不是函数调用的位置
    function fn2() {
      console.log(a)//1
    }
  </script>
</body>

</html>